Masters Degrees (Geology)

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Open Access
The allanite deposits on Vrede, Gordonia District, Cape Province
(University of the Free State, 1961-11) Hugo, Petrus Jacobus; De Villiers, J. E.; Kent, L
Allanite deposits of an unusual nature occur in two types of granulite on the farm. Vrede, portion of Cnydas West, Gordonia District, Cape Province. The granulites belong to the Archaean complex which is also represented by schists and gneisses. These rocks, which are described in detail, have been correlated with the Kaaien Series of the Kheis System. The ore bodies are characterised by their distinct banding and the close -connection between their distribution and the regional structure of the metamorphic rocks. Allanite occurs with tourmaline, apatite, zircon and monazite in bands ranging from one-sixteenth to two inches in thickness, parallel to the foliation of the granulites. The mineralisation, probably hydatopneumatolytic in nature, started with the introduction of zircon, monazite and tourmaline, after which apatite, allanite, magnetite and quartz followed in that order. The optic axial angle of the allanite is 2V=60° or more. A high magnesian variety, however, has a positive sign with 2V=40°. The range in refractive indices is: no~=1.732 - 1.757 n f3 = 1. 7 4 7 1. 7 68 n~ = 1.759 1.779 This variation is probably due to differences in chemical composition. The three analyses of allanite given have been recalculated on the basis of 13 (O, OH, F) atoms to the unit cell and the formulae obtained conform closely to the formula X₂ Y₃ Z₃ (O, OH, F) 13 developed by Machatschki. Chip sampling was done on all the deposits and the samples were radiometrically assayed against a standard uranium-thorium sample. The average values obtained are Allanite is, therefore, a prescribed material in terms of the Atomic Energy Act. The other ore minerals are all normal in their properties. A crystallising pegmatite is believed to have been the source of the mineralising, solutions giving rise to these deposits. This pegmatite and those of the surrounding area are related to a younger granitic intrusion, probably the acid granite intruded into parts of Bushmanland. The deposits opened up by 1960 occur intermittently over a total area of approximately 600 feet by 200 feet, but their extent in depth has still to be proved. Only the main deposit may perhaps be workable; if the allanite bands there extend to a depth of 200 feet, the ore reserve will be of the order of 1500 tons, assuming that the ore contains roughly 10 percent allanite.
Open Access
Die geologie van die serie Stormberg in die sisteem Karoo, suid van Bethlehem, O.V.S.
(University of the Free State, 1964-08) Kingsley, Charles Seymour; Van Biljon, W. J.
Afrikaans: 'n Gebied tussen Bethlehem en Fouriesburg, waarin alle etages van die Etage Bo-Beaufort tot die Etage Drakensberg verteenwoordig is, is gekarteer asook die veldgegewens opgeteken. Oor geskikte roetes in die gebied is monsters geneem waarop verskillende petrografiese ondersoeke gedoen is. Vanaf swaarmineraalstudies kon gevolgtrekkings gemaak word omtrent oorspronggebied en afsettingstoestande van die Serie Stormberg. Korrelgrootte en -verspreiding is in die sandstene deur sifanalise bepaal. 'n Vergelykende studie is met behulp van die mikroskoop op die sandstene sowel as op die dolerietindringings en lawavloeiings uitgevoer. Uit die resultate kon in hooftrekke die volgende afleidings gemaak word: Die oorsprongrotse van die sedimente moes hoofsaaklik vanaf granitiese stollingsgesteentes wat êrens na die suidooste geleë was afkomstig gewees het. Die afsetting van die sedimente moes in landelike meergebiede geskied het. Die Moltenolae se afsetting moes relatief vinnig onder nat toestande plaasgevind het, terwyl die Eooilae en Holkranssandsteen onder 'n geleidelike droeër-wordende klimaat gevorm is. Die laaste stadiums van afsetting van die Holkranssandsteen het gelyktydig met die eerste lawavloeiings plaasgevind. Laastens was die dolerietgange in hierdie gebied moontlik ook die toevoerkanale vir die basaltiese Drakensberglawa.
Open Access
Die sedimentologie van die Etage Holkranssandsteen, sisteem Karoo
(University of the Free State, 1969) Beukes, Nicolas Johannes; Visser, J. N. J.
Afrikaans: 'n Regionale, sedimentologiese studie van die Etage Holkranssandsteen is gedurende Maart 1968 tot Maart 1969, in Natal, Noordoos-Kaapland, die Vrystaat en Lesotho, voltooi. Die etage is in drie rotsstratigrafiese sones, gebaseer op 45 stratigrafiese profiele, ingedeel. Sone I bestaan uit dik- tot baie dikgelaagde, massiewe, baie fynkorrelrige sandsteen tot sanderige sliksteen. Die kontak met die Etage Rooilae is aan die basis van die deurlopende, massiewe sandsteen geneem. Dit is egter nie 'n vaste kontak nie, aangesien daar 'n geleidelike oorgang tussen die Rooilae en holkranssandsteen bestaan. Sone I bereik sy maksimum dikte in die noorde van die geboed en hier word dit veral deur 'n ligbruin of ligrooi kleur en volop kalsitiese konkresies gekenmerk. Holkranse kom algemeen in die sone voor. Hulle vorm deurdat die sandsteen wat 'n kalsitiese matriks bevat, makliker verweer. Klein, lensvormige afsettings met vlakwaterstrukture word dikwels aangetref. Sone II kan as 'n Kruisgelaagde Sone beskryf word. Dit bestaan uit kruisgelaagde en fynbelaagde, relatief growwer, skoon sandsteen tussengelaagd met massiewe, baie fynkorrelrige, vuil sandsteen. Lensvormige afsettings met kenmerkende vlakwaterstrukture is relatief skaars. Sone III bestaan hoofsaaklik uit massiewe, dik- tot baie dikgelaagde, vuil, baie fynkorrelrige sandsteen in die noorde en weste van die gebied. Na die ooste en suide gradeer die sandsteen lateraal in ligbruin en ligrooi, massiewe, dik- tot baie dikgelaagde, slikkerige sandsteen en sanderige sliksteen met volop klein kalsitiese konkresies. Lensvormige afsettings met kenmerkende vlakwaterstrukture kom algemeen voor, maar is veral opvallend op die kontak met die Drakensbergbasalt. Sandsteenlae kom tussengelaagd met die basalt voor en dui daarop dat die sedimentasie nie volledig met die eerste lawavloeiings beëindig is nie. Sedimentasie het in 'n vlak, binnelandse kom plaasgevind. Die afsetting van die Holkranssandsteen het waarskynlik vroeër in die noorde as in die suide van die gebied begin. Dit kan aan 'n geleidelike verskuiwing van klimaat (gekoppel aan Kontinentale Drywing of Poolverskuiwing) toegeskryf word. Die etage bereik sy maksimum dikte in die suidelike deel van die gebied. Die lokale veranderings in dikte is deur die uitvloei van lawas, wat sedimentasie beïnvloed het, en primêre duinstrukture veroorsaak. Die kruisgelaagde eenhede van Sone II kan aan die migrasie van duine toegeskryf word. Die brongebied van die sedimente was na die weste, noordweste en suidweste geleë en het hoofsaaklik uit sedimentêre materiaal van die Serie Beaufort bestaan. Die korrelgrootte van die kruisgelaagde sandsteen neem in die rigting van afsetting af. Die massiewe sandsteen dui op meer stabiele duine na afsetting, deurdat hulle nie herhaaldelik herwerk is nie. Strukture in die sandsteen word deur verwering of die uniformiteit in korrelgrootte verberg. Duine versadig met water het moontlik tot sandvloeiings en die vernietiging van strukture aanleiding gegee. Die korrelgrootteverspreidings van die sandstene stem met die van eoliese sedimente ooreen. Die kwartskorrels in die gesteentes is hoofsaaklik afgerond, maar die primêre afronding is deur diagenese verlaag. Die korrels besit gematte of pokdalige oppervlakke en dit word aan fisies-chemiese prosesse wat in woestyne teenwoordig is, toegskryf. Die sandstene is halfvolwasse en kan hoofsaaklik as sub-grouwakke geklassifiseer word. Die kruisgelaagde sandsteen is beter gesorteer en meer grofkorrelrig as die massiewe sandsteen. Die mineralogiese samestelling dui daarop dat die sedimente van die drie sones vanaf dieselfde brongebied afkomstig is. Seoliete kom in sommige van die sandstene voor en hulle is aan die vulkaniese aktiwiteite verwant. Die afsetting van die drie sones kan aan klimaatsveranderinge gekoppel word. Sones I en III is onder halfdroë woestyntoestande afgeset, terwyl 'n droë klimaat, soortgelyk aan die van 'n ware woestyn, tydens die afsetting van Sone II geheers het. Ten spyte van die droë klimaat het plante- en dierelewe, tot en met die uitvloei van die eerste lawas van die Etage Drakensberg, bly voortbestaan.
Open Access
A sedimentological study of the conglomerates in the Elsburg stage on the Welkom and Western holdings gold mines
(University of the Free State, 1970-12) Kleynhans, Jacob Johannes; Botha, B. J. V.; Visser, J. N. J.; Antrobus, T.
A sedimentological description of the layers of conglomerate in the Elsburg Stage of the Witwatersrand System, as disclosed by 23 boreholes and underground development on the Welkom and Western Holdings Gold Mines in the Orange Free State Goldfield, is given. The palaeocurrents in the Elsburg Stage as inferred from pebble-size distribution and preferred pebble orientation, were from two different directions. On Western Holdings Limited and the Welkom Mine area west of the Arrarat Fault, the layers of conglomerate were derived from the north-west. On the Welkom Mine area east of the Arrarat Fault, the direction of transport was from the south-west. These two different palaeocurrent directions can be explained by lateral movement along the Arrarat Fault. Thus, the eastern block of the lease area of the Welkom Gold Mining Company, which was formerly situated on the north-eastern flank of a delta fan, was displaced along the strike of the Arrarat Fault for a distance of approximately 6 000 m towards the south, while the western block (Welkom No.3 Shaft and Western Holdings Limited), was displaced towards the north. A detailed analysis regarding the composition, roundness, shape, orientation and sorting of the pebbles in the layers of conglomerate was undertaken. The sorting and roundness of the pebbles increase towards the centre of the basin, while the majority are orientated with their long axes parallel to the palaeocurrent direction. The percentage of non-durabIe pebble types also decreases in a down-current direction, while the durable types remain constant. The pebbles are mostly spheroidal, although certain types show a strong tendency to disc shaped. These features indicate that the layers of conglomerate were probably deposited on an alluvial fan bordering an inland lake or sea.
Open Access
Die geologie van die gebied Poortjie 3022B in die distrikte Britstown, Carnarvon, Prieska en Victoria-Wes, Noord-Kaapland
(University of the Free State, 1977) Van der Westhuizen, Willem Andries
Die geologiese geskiedenis van die gebied was kompleks en word gekenmerk deur verskeie diskordansies en klinodiskondansies asook vulkanisme, vervorming, metamorfose en vergletsering. Die oudste gesteentetipe is die Welgevondengraniet, 'n horst, wat as vloer beskou word. In die noordoostelike hoek van die gebied dagsoom dolomiet; kalksteen en gestreepte ysterformasie van die Sisteem Transvaal. Wes van die Doornberglineament dagsoom gesteentes bestaande uit arkoose, lawa, kalksteen en gestreepte ysterformasie wat vroeër as 'n gedeelte van die Serie Marydale beskou was, maar wat nou die Soetvleiformasie genoem word, en wat 'n ouderdom vergelykbaar met die Transvaalgesteentes het. Die geochemie van die Soetvleilawas dui 'n tholeiïetiese basaltiese samestelling aan. Die lae van die Sisteem Transvaal knyp uit teen die Welgevondengraniet en gevolglik kan die Welgevondengraniet as ‘n gedeelt e van die westelike grens van die Transvaalkom beskou word, of dit kan in hoog in die. Transvaalkom wees met 'n laterale variasie in die litologie wes van die hoog af. Wes van die Welgevondengraniet is daar 'n dik opeenvolging van metapelitiese gesteentes bestaande uit kwartsiete, gneise en amfiboliete wat met die Matsap/Kheis gekorreleer word. Die graad van metamorfose is egter eerder vergelykbaar met dié van die Namakwalandse Mobiele Gordel as met die Kheis- of Matsapdomein verder noord. Die gesteentes het drie hoofperiodes van vervorming ondergaan waarvan die eerste twee isoklinaal ko-aksiaal was, met ‘n noord-noordwestelike strekking, gevolg deur 'n periode van oopplooiing loodreg op die b-plooias van die eerste twee periodes van vervorming. Hierdie laaste periode van plooiing het koepel-en-kom strukture tot gevolg gehad. Die gesteentes wes van die Doornberglineament was aan verskeie temperatuur- en druktoestande blootgestel en gevolglik kan twee isograde deur die gebied getrek word. Daar is 'n toename in graad van metamorfose van oos na wes en die metamorfe gebiede bestaan uit baie laegraadse-, laegraadse- en 'n medium- tot hoëgraadse area. Na die tydperke waartydens vervorming en metamorfose plaasgevind het, het 'n glasiale periode begin waartydens die Serie Dwyka afgeset is. Uit die voorkoms van halietkristalle in die Étage Bo-Dwykaskalies kan afgelei word dat die afsetting van dié Serie onder vlakwatertoestande plaasgevind het en nie in 'n relatief diep see soos aanvanklik vermoed is nie. Na die afsetting van die Karoosuksessie het doleriet, en nog later, kimberliet die Karoogesteentes binnegedring. Die Karoogesteentes word grootliks deur resente materiaal soos kalkreet, sand en grond bedek. Ondergrondse water is geassosieer met verskuiwings en lineêre strukture en goeie lewerings kom voor. Geormorfologies bestaan die gebied uit groot vlaktes met inselberge. Die vernaamste erosiesiklusse was die Afrika- en na—Afrikasiklusse.
Open Access
Die geologie in die omgewing van Britstown
(University of the Free State, 1977) Lemmer, William Murray
Afrikaans: 'n Stratigrafiese kolom is met behulp van geologiese kartering en profiele vir die gebied opgestel. Die twee eenhede van die Ventersdorpgroep kan gekorreleer word met die eenhede in die Bothaville-omgewing. Die nuwe standaard onderverdeling van die Karoosupergroep wat in die gebied gebruik is, verskil van die ou indeling. Paleogeomorfologiese gegewens en primêre strukture toon dat die Dwyka-ysplate in 'n suid-suidoostelike rigting beweeg het. Verskillende afsettingsomgewings soos diep mariene, onderste wegstrand, boonste wegstrand, strandfase, delta-top en kontinentale fluviale omgewings kan in die veld vir die Ecca- en Beaufortgroepe onderskei wrod. Primêre strukture, petrografiese en paleontologiese gegewens dui op 'n diep mariene, beperkte afsettingskom vir die Prins Albertformasie. Die Whitehill- en Tierbergformasies is onder soortgelyke toestande afgeset. Die water het vlakker geword en deltas wat die begin van die Beaufortsedimentasie aandui, het vanuit die suidweste gemigreer. Kontinentale fluviale sedimente is op die sikliese deltaïese sedimente afgeset. Die kontak tussen die Ecca- en Beaufortgroepe is graderend en vir praktiese doeleindes is die basis van die eerste deurlopende sandsteenlaag aan die bokant van die Eccagroep konsekwent as 'n herkenbare en karteerbare eenheid in die veld as kontak geneem. 'n Enkele kimberliet wat nie vantevore beskryf is nie, is gevind. Die verspreiding van kalkreet word beheer deur die topografie en kom net op ou Afrika-oppervlakke voor.
Open Access
Die sedimentologie van die Soutpansbergsteenkoolveld met spesiale verwysing na steenkoolvorming
(University of the Free State, 1980) Van der Berg, Hendrik Jacobus; Visser, J. N. J.
Afrikaans: Die Karoolae noord van die Soutpansberg is geleë in die Tshipise-kom wat tydens vorming deur oos-wesverskuiwings beheer is. 'n Hoë rug in die vloer verdeel die kom in die weste in 'n suidelike en 'n noordelike trog wat onderskeidelik deur kwartsiet en lawa van die Soutpansberggroep en ouer tuf onderlê word. Die kom is waarskynlik met die swak sone, geskep deur die Limpopo Mobiele Gordel, geassosieer. Na-Karooverskuiwings het 'n rol gespeel in die behoud van die Karoo-lae in die Tshipise-kom. Die Karoo-opeenvolging is litologies in 6 sones verdeel en die sedimentasie van die sones is deur middel van vertikale siklusse bestudeer. Sone 1, aan die basis, bestaan uit 'n onderse Sanderige en 'n boonste Kleiige Diamiktieteenheid. Die Sanderige Diamiktieteenheid word opgebou ui oorwegend diamiktietlae bestaande uit fragmente, enkeles geskraap en gefasetteer, van kwartsiet, lawa en tuf van wisselende grootte in 'n sanderige matriks. Dun warfagtige lae kom soms ook voor. Die eenheid word geïnterpreteer as 'n oorwegend fluvioglasiale afsetting, agtergelaat deur valleigletsers wat ooswaarts teruggetrek het. Fasiesveranderinge kom algemeen in 'n weswaartse rigting voor. Die Kleiige Diamiktieteenheid bestaan oorwegend uit koolstofryke, kleiige sedimente wat waarskynlik ook vanuit die ooste aangevoer is. Grofkorrelrige, sanderige materiaal was egter ook vanaf die sentrale rug in die weste afkomstig en is as kanaalafsettings tussen die kleiige lae afgeset is. Langs die steil afsettingshellings het moddervloeie ontstaan en 'n vermenging van grofkorrelrige en kleiige materiaal het tot die kleiige diamiktietlae aanleiding gegee. Sone 2 bestaan uit sandsteen, skalie-sliksteenassosiasie, moddersteen en steenkool, oorwegend in opwaarts fyner-wordende fluviale siklusse gerangskik. Die sedimente is hoofsaaklik deur meanderende rivieriere op die vloedvlakte as puntwal-, oewerwal- en deurbreekafsettings agtergelaat. Die sandsteen-skalieverhouding van die opeenvolging dui op 'n aanvoerrigting vanuit die noordooste. Tydens kort stabiele periodes het plantmateriaal in vloedkomme onder koel, redusereende toestande versamel en tot dun, afwisselende steenkoollae aanleiding gegee. Die baie wortelafdrukke, paleosols, tussengelaagde skalie en siklisiteit van die steenkoollae dui op 'n oorwegend in situ oorsprong vir die steenkool. Sone 3 volg diskordant op Sone 2 en bestaan uit 'n onderste grofkorrelrige Sandsteeneenheid, opgebou uit opwaarts fyner-wordende siklusse en is deur vlegstrome vanuit die suidooste afgeset. Dit gradeer in 'n Moddersteeneenheid bestaande uit dun opwaarts fynerwordende sandsteensiklusse en dik, grys tot koolstofryke, kleiige gedeeltes. Die afsettingshelling het platter geword en die eenheid is afgestet deur meanderende riviere met wye vloedvlaktes. Hoewel die litologie en sikliese ontwikkeling van Sone 4 presies met dié van Sone 2 ooreenstem, is die gesteentes van Sone 4 oorwegend rooi, pers en groen van kleur en plantmateriaal is afwesig, terwyl karbonaatryke knolle opwaarts in die sone meer algemeen word. Dit dui op afsetting deur meanderende strome vanuit die suide en suidooste tydens warm en droër klimaattoestande. Sone 5 bestaan uit 'n middelkorrelrige, goedgesorteerde sandsteen. Sone 5 bestaan uit 'n middelkorrelrige, goedgesorteerde sandsteen. Sedimentêre strukture aan die basis dui op afsetting deur water, maar hoër op kom uitsluitlik grootskaalse wig- en tafelvormige kruisgelaagdheid voor en word die lae as 'n windafsetting geïnterpreteer. Woestyntoestande het dus op daardie tydstip geheers en die heersende windrigting was vanuit die suidweste. Karoosedimentasie is deur die uitvloei van basiese lawa (Sone 6) en die indringing van dolerietplate en -gange afgesluit. Die Karoolae in die Tshipise-kom kan met dié in die hoof-Karookom gekorreleer word. (i) Die Sanderige Diamiktieteenheid word op grond van afsettingsomgewing en stratigrafiese posisie met die Dwykaformatsie gekorreleer. (ii) Die Kleiige Diamiktieteenheid verteenwoordig 'n oorgangsfase, maar word saam met Sone 2, waarin fossiele van Glossopteris en Vertebraria algemeen voorkom, met die Eccagroep gekorreleer. (iii) Sone 3 word op grond van litologie en die voorkoms van Dicroidium sp. met die Moltenoformasie gekorreleer. (iv) Sone 4 word met die Ellitoformasie gekorreleer. (v) Sone 5 word met die Clarensformasie gekorreleer. (vi) Sone 6 stem ooreen met die Drakensberggroep. Die Beaufortgroep is volgens hierdie indeling afwesig in die Tshipise-kom.
Open Access
The geology of an area west of Welkom, O.F.S.: (degree blocks 2825 A and B and 2826 A)
(University of the Free State, 1980-10) Behounek, Norbert Josef; Grobler, N. J.
Rocks present in the mapped area range from Early Precambrian (Easement granite) to the most recent deposits of aeolian sands, alluvium, gravel and calcrete. Outcrops of Ventersdorp rocks are scarce and widely scattered. Nevertheless, agglomerates and felsic lavas of the Makwas'sie Quartz Porphyry Formation, fanglomerates, .quartzites, volcanic breccias, tuff, mafic massive la.vas and pillow lavas of the Rietgat Formation, quartzites of the Bothaville Formation and plateau lavas of the Allanridge Formation could be distinguished and studied. The latter were all grouped together in accordance with the lithostratigraphic classification of Winter (1976), because of the proximity to his type area. Overlying the Ventersdorp Supergroup are shales and/or tillite of the Karoo Sequence. Bore holes drilled to the east (outside) of the mapped area proved that Dwyka glacial deposits are preserved in pre-Karoo valleys and/or valleys excavated through ice movement. Here, the Dwyka Formation consists of tillite, varved shales and a glacio-fluvial unit, viz. the sandstone-siltstone-shale unito In the western sector of the mapped area. Ventersdorp rocks are directly overlain by black, micaceous shales of the Ecca Group (Prince Albert Formation). The V/hitehill .Formation is probably not present as one continuous layer over the whole of the mapped area, and only occurs in a few isolated pockets. As a result the Prince Albert Formation is in most cases overlain by grey shales of the Tierberg Formation which grades from shales and mudstones (marine deposits) upwards into rhythmic layers of grey shales and sandstones (deltaic deposits). The transitional zone between the Ecca Group (Tierberg Formation) and the overlying Beaufort Group is exposed on the farm Basberg 416. The Beaufort Group in this area shows the typical features of a fluvial deposit, viz. coarse-grained channel-axis facies which laterally grade into finer-grained and thin-bedded hannelmarginal facies and levee mudstone deposits. The latter sediments were most probably deposited on the flood plain of a braided rivero Intrusive rocks consist of post-Karoo dolerites (sills and dykes) and the kimberiite intrusions at Rovic Diamond Mines. Nodular and laminated calcrete deposits are the most abundant calcrete deposits in the area under investigation, Aeolian sands cover large tracts of this area and occurmaiicly as aeolian sheet deposits but also as dunes of variable magnitude. The Vaal River Gravels and the alluvial sands and silts of the Yet and Sand Rivers are the most significant alluvial deposits present in the mapped area. Pans of variable shaper, and sizes have originated through the erosion of paleo river channels by subsequent wind action.
Open Access
The source material of the Big Pebble Marker and Rosedale reefs in the Welkom Goldfield
(University of the Free State, 1990-06) Steenekamp, Johannes Marthinus Andries; Grobler, N. J.
English: In this study the clasts of the Big Pebble Marker (BPM) in the Aandenk Formation and the basal conglomerate of the Rosedale Member (ROM) in the Eldorado Formation, in the Welkom Goldfield, were investigated. The aim of this study was to employ a different approach to acquire an insight into the nature of the provenance of the gold-bearing conglomerates in the Welkom Goldfield. To achieve this, the quantitative and qualitative compositions of two coarse and polymictic reefs were studied. Observations were made at six underground IocaIities per reef. At each locality a clean, reasonably flat surface, of three to four square metres, with sufficient conglomerate exposure, was investigated. A modal count of the different types of clasts present was done at one thousand points per exposure with the aid of two grid frames. The long axes of at least two hundred clasts, falling on preselected lines, were measured. The long axes of the ten largest clasts in the selected area were also measured. Representative samples of the various clast types present were taken for laboratory study. Every exposure studied, was photographed. All samples were cleaned meticulously to prevent any contamination with matrix material. A total of 126 samples were analyzed for gold, major and trace elements. A selection of samples were also analyzed by means of XRD and microprobe for mineral composition. Petrographic studies were carried out on thin sections of all the samples. A few samples were investigated by means of electron microscope. Fluid inclusion studies were carried out on four quartz samples. All the field data and analytical results were processed statistically plotted on concentrations on computer. Petrographic information were standard ternary diagrams. Average gold in the different clast types were compared with world wide averages for comparable rock types. Field data indicate different transport mechanisms for the BPM and RDM. Composite or multiple provenances are also indicated for both reefs. Quartz and chert dominate the clast assemblages of both reefs, but more so in the case of the BPM. Results from the clast assemblage plots on the ternary diagrams indicate thrust belt and recycled orogenic provenances for the BPM and RDM. Clasts, derived from greenstone-type source rocks, occur predominantly in both reefs. Silica dominates the chemical composition of the majority of the clasts. On average, chert clasts from the BPM contained the highest gold concentrations (143 ppb) of all the clast types. Based on modal composition, the total c last assemblage of the BPM is approximately 6X more auriferous than that of the RDM (76 ppb vs 12 ppb). Respectively, these figures are approximately 30X and 5X higher than the figure of 2,4 ppb, which is generally accepted for a Barberton-type granite-greenstone crust.
Open Access
The development and application of key profit drivers in mineral resource management
(University of the Free State, 2002-02) Van Niekerk, Gerhardus Johannes; Van der Westhuizen, W. A.; Boer, R. H.
Every mining operation is constantly seeking for new ways to manage a broad range of business variables. Managers across the production chain find themselves torn between the initiatives to reduce costs, balancing throughput and asset utilisation improvements, maintaining product quality, and other similar performance indicators. This they do in their respective areas of responsibility, measuring against their set targets. Herein lies the dilemma: Which operational factors will maximise the profit of the organisation as a whole as opposed to the individual areas. And what is the impact of parameters outside their domains on their performance areas? Phalaborwa Mining Company has been no exception in this scenario. With time the same issues and operational challenges were presenting itself to the management team. The question had to be asked: Would a fundamentally new approach to viewing the business unearth anything new and useful to take this remarkable company to new heights? This study was launched to challenge the views of business and to offer answers to the above dilemma. The study has shown a remarkable degree of interlinkedness between production variables across the production chain. For instance, the mineralogy and petrology of the rock mined had strong effects in the milling, flotation and even smelting processes, and the status of the metal market price conditions offered exciting options to operational managers, provided the relationships are understood. Using an integrated model the magnitude and nature of interrelationships between the drivers of performance are explained. As a result it could provide the capability to "play off' costs against benefits for operating decisions. For example: How long should one keep the open pit mine operational and should it be decommissioned at the same or at a different time as the downstream units? The integrated nature of the business model clearly showed that to reach optimal performance for the whole company, decision-makers across the production chain need to plan collaboratively. It was evident that the powerful modelling approach will loose its effectiveness if the organisational thinking is not changed to a collective one. The model therefore, could only be effective if it is embedded into the planning and monitoring business cycles.
Open Access
Assessment of potential toxic influence of uranium trial mining in the Karoo uranium province
(University of the Free State, 2003) Scholtz, Nicolaas; Loock, J. C.
An assessment of uranium trial mining on four mining sites in the Karoo Uranium Province, South Africa revealed localised above-background values for U, Mo, Pb, Cu, As and Fe in surface - and ground water, soils, sediment and crops. Inadequate remedial action on cessation of mining activities in 1980 led to the presence of uranium ore in stockpiles, open pits, mining shafts, mining equipment and waste dumps within featured areas. Heavy metal contamination is suppressed by the lack of run–off and the dry climate experienced within the mining areas. However, the heavy metal content in surface water and sediment within the open pits on Rietkuil and Mooifontein is especially high. These values pose a risk for human ingestion and may cause cancer in the long term or renal damage over the short term. These pits are easily accessed, lack a fence and are used for a drinking medium by fauna and as a growth medium for flora. The easily accessed Cameron Shaft on Ryst Kuil is a matter of concern due to the possible presence of the radioactive inert gas, radon. Farm owners were unaware of the possible toxic effects of uranium and coherent heavy metals. This led to previous usage of mine water for crop irrigation, the moving and feeding of livestock as well as wildlife amongst uranium ore stockpiles, swimming in water-filled open pits and using crushed uranium ore for gravel road maintenance and construction. The presence of uranium ore in stockpiles and the coherent effects on the water, soils, sediment, fauna and flora and possibly man, prioritises the remediation and rehabilitation of the of uranium trial mining sites within the Karoo Uranium Province.
Open Access
Quantitative evaluation of minerals in coal deposits in the Witbank and Highveld Coalfields, and the potential impact on acid mine drainage
(University of the Free State, 2003-05) Pinetown, Kaydy Lavern; Van der Westhuizen, W. A.
A mineralogical and geochemical study on the coal and coal-bearing successions of the Witbank and Highveld Coalfields in the Mpumalanga Province of South Africa was proposed in order to, firstly, investigate the quantitative distribution of minerals in the lithological units, and secondly, to correlate this data with the potential of the units to contribute to acid mine drainage conditions in the region. X-ray diffraction and X-ray fluorescence techniques were used to analyse the samples from the study area. Samples from the No.1, No.2, No.4 and No.5coal seams were collected from several mines in the Witbank Coalfield, while samples from the No.4 and No.5coal seams were collected from borehole material obtained from the Highveld Coalfield. The inorganic components make up approximately 8.00 to 35.00 wt% of a coal sample. Si02 concentrations varied between 0.00 and 35.00 wt% of a sample, AI203 between 0.50 and 16.00 wt%, Fe203 between 0.03 and 10.00 wt%, and S between 0.15 and 8.00 wt%. Minor concentrations of CaO (0.00 to 8.00 wt%) and MgO (0.00 to 1.00 wt%) were present. P205 occurred in concentrations of 0.00 to 3.50 wt% and K20 was in the order of 0.00 to 1.30 wt%. Na20 values were the lowest varying between 0.00 and 0.45 wt%. The only difference in chemistry between Witbank and Highveld coals was a slight increase in Na20 (0.00 to 0.51 wt%) in the Highveld coals. These results were confirmed by the XRD investigations. The mineral components in the XRD patterns were semi-quantitatively evaluated in terms of dominant (>40% of the mineral fraction), major (10-40%), minor (2-10%), accessory (1-2%) and rare « 1%) constituents. The mineral fraction in the coals was dominated by quartz and kaolinite, with major to minor and trace amounts of calcite, dolomite and pyrite, as well as accessory phosphates phases. XRF and XRD results for the coal-bearing units were also in good agreement. Higher K20 and Na20 concentrations were obtained in the sandstones in comparison to the siltstone and carbonaceous shale samples, and were supported by the presence of feldspars and clays such as illite in XRD interpretations. A normative program designed for Australian coals and sedimentary rocks, called Sednorm, was used to calculate normative mineralogical compositions from the geochemical results. Good \ correlations were obtained for comparisons made between the chemical composition, mineralogical interpretations and normative results for the coal and sediment samples. Acid-base accounting was used to investigate the potential of the coal and coalbearing units to produce acid mine drainage conditions. The acid and neutralising potentials are largely dependant on the abundance and availability of minerals such as pyrite and calcite respectively. According to the screening criteria proposed by Usher et al. (2001), averages for Neutralising Potential Ratio (NPR) suggest that all the coal and coal-bearing units, excluding the unit between No. 1 and No. 2 coal seams, are potentially acid generating. The latter lithological unit is considered to be inconclusive. The average Net Neutralising Potential (NNP) values suggest that the NO.5 coal seam, NO.4 Upper coal seam, and between NO.4 and NO.2 coal seams are potentially acid generating. This is a result of the weathering of carbonates in these lithological units. The other units could become either acidic or neutral. In theory it is possible to calculate the AP from the analysed S by multiplying the S value by 31.25. Assuming that all sulphide-S is available for oxidation, then the total S analysed could be used to predict the AP for samples on which no acid-base determinations has been carried out. Similarly, the excellent correlation between the NP and CaO, and between the NP and combined CaO and MgO, confirms that these chemical components are largely responsible for NP values. It is then also possible to predict the NP by using the CaO and MgO concentrations for samples for which no AP or NP data is available. The application of ABA in this study offered a major contribution to understanding the complexities governing water-rock interactions. Results provided a preview of situations that might arise regarding groundwater quality in a certain area, but also offers ample time to decide on appropriate prevention or remediation programs. The potential for these lithological units to contribute to the deterioration of groundwater is evident.
Open Access
The relationship between geological structures and dolerite intrusions in the Witbank Highveld Coalfield, South Africa
(University of the Free State, 2008-05) Du Plessis, Gideon Petrus; Praekelt, H. E.
English: The study forms part of the COALTECH 2020 research program, a collaborative study which aims to ensure the continued viability of the South African Coal Mining Industry well beyond the year 2020. It participates in the Geology and Geophysics Technology Area of the COALTECH 2020 Technology Wheel. The mission statement of this Working Group is to facilitate applied research to identify, quantify and qualify the remaining Coal Resources, starting with the Witbank-Highveld Coalfield, to enable informed decisions when defining and extracting Coal Reserves. The structural investigation of dolerites in the south-eastern part of the Witbank Coalfield contributes to Task 1.1.1; Sedimentological and Structural Model of the Witbank-Highveld Coalfield. The Witbank Coalfield in the Mpumalanga Province of South Africa is situated on the northern sector of the main Karoo basin. The main Karoo basin is described as an asymmetric depository with a stable, passive cratonic platform (Kaapvaal Craton) in the northwest and a foredeep to the south with the Cape Fold Belt on its southern margin. The study area is situated south of the prominent  15m thick Ogies Dyke, which strikes from Ogies in the west to Optimum Colliery in the east. The east-west trending pre-Karoo Smithfield Ridge, consisting of Rooiberg Felsites, bounds the study area to the south and also separates the Witbank Coalfield from the adjacent Highveld Coalfield to the south. The study was conducted on four collieries, namely Bank, Goedehoop, Koornfontein and Optimum Collieries in the south-eastern part of the Witbank Coalfield. The objective of the study is to investigate the intrusion mechanism of the dolerites and the metamorphic effect the dolerite intrusions had on the coal in order to quantify the impact on mining and coal utilisation in the south-eastern part of the Witbank Coalfield. The most important effects of dolerites on mining with a decreasing order of importance are: 1. Decrease in the safety conditions and an increase in the risk of roof failures, pillar and floor stability. 2. Increase in the overall production and mining costs with a decrease in the potential profit. 3. Decrease in saleable tonnages with a decrease in the profit margin. 4. Increase in waste product generation and an increase in the environmental risk. From the objective two separate studies were identified: the first study (A) focuses on the relationship between geological structures and dolerite intrusions and the second study (B) determines the metamorphic effect the dolerite intrusions had on the coal. The structural investigation of the relationships between geological structures and the dolerites is contained in this document. Regional scale information was acquired by using various remote-sensing techniques. The CSIR Miningtek through the COALTECH 2020 Research Program provided this state of the art information. In conclusion to the regional scale study probable relationships between certain Karoo-age dyke, sill and lineament trends that are associated with the northern main Karoo basin and surroundings could possibly provide insight into better understanding of the intrusion mechanism of dolerites in the south-eastern Witbank Coalfield. It is therefore probable that some of the Karoo-age intrusives in the south-eastern Witbank Coalfield followed older basement structures inherited by the Karoo strata and/or syn-tectonic structures related to Gondwana fragmentation which was synchronous with dolerite intrusion (Encarnación et al., 1996). The EW striking Ogies Dyke, which is the main structure in the Witbank Coalfield, most probably pre-dates its associated smaller scale dykes and sills. Conclusions for this relative age difference are summarised as being the following: Its association with EW basement Pre-Karoo diabase, which probably acted as a plane of weakness and might have triggered its earlier intrusion. Difference in geochemical and mineralogical characteristics. Absence of sills immediately to its north. Should the NS striking dykes north and south of the Ogies Dyke be favoured by cooling joints which developed as a result of its earlier intrusion, the age difference is evident. Comparing the physical appearance of the ± 20m sill (main sill) in the Witbank Coalfield with the B8 sill in the Secunda Coalfield, the two sills have a number of properties in common. However, these physical property comparisons are not precise and it is therefore suggested a detailed geochemical analysis be undertaken focussing on the mineralogy, major and trace elements. The sedimentary sequence is reconstructed by removing the main sill from the stratigraphy. The reconstruction is aimed at determining if a spatial relationship exists between the coal seams, the intra-seam strata and the main sill prior to the intrusion event. Borehole information on the elevation of the pre-Karoo basement is sparse as borehole penetration was terminated at the bottom of the coal seam of interest. The removal of the dolerite convincingly reveals the pre-Karoo basement topography, palaeo-floor and -roof morphology, as well as the width distribution of the sedimentary units. The following reconstructed sedimentary units were examined individually: No. 2 Coal Seam; Facies between the No. 2 Coal Seam and No. 4L Coal Seam; No. 4L Coal Seam; Facies between No.4L and No. 5 Coal Seam; No. 5 Coal Seam. The examination process of the data of each unit starts with the statistical analyses thereof which includes histogram and probability plots of the palaeo floor, width and palaeo roof. The investigation resulted in nearly direct linear correlation curves which disclose the existing relationships between the palaeo floor elevations of the No.2, No.4L and No.5 Coal Seams. Considering the range of correlation coefficient values of 0.81 to 0.99 for the palaeo floor elevations it convincingly reveals the co-existing relationship in the geometry of elevations throughout the entire stratigraphy of the sedimentary sequences. Several sedimentological factors contributed to the present day geometries and widths of coal and associated clastical sedimentary rocks of sequence of succession. The evidence in the relationship of the geometries of the palaeo floor and roof elevations concludes that irrespective of variable intra-seam strata and coal seam widths the pre-Karoo topography is reflected throughout the entire stratrigraphic sequence. Prior to sediment burial, plant growth took place most probably on similar structural relief of gentle attitudes. To conclude, a four-stage model is proposing how burial could have influenced widths and aerial distribution of peat and intra-seam clastic sedimentary rocks of sequence of succession. At the time of peat formation, the unconsolidated sediments had not yet undergone a great deal of lithification in that the floor structure of the peat might have been without undulations. In conclusion, a reasonable inverse relationship between the net width of the stratigraphic sequence from the palaeo floor of the No. 2 Coal Seam to the palaeo roof of the No.5 Coal Seam and the floor elevation of the main sill exists. A Quantile-Quantile-plot and the regression slope analysis of the data sets convincingly conclude the inverse relationship that exists between the floor elevation of the main sill and the net width of the almost entire sediment sequence. In this context the reasonable negative correlation coefficient of -0.57 is good. This negative correlation implies that where the main sill is present in the lower stratigraphic levels it underlies thicker sedimentary sequences and conversely where the sill had stepped up to higher stratigraphic levels it underlies the thinner sedimentary sequences. In conclusion the differential compaction of the sedimentary strata was in the main controlled by the the Pre-Karoo basement topography. This in turn resulted in the fracturing and jointing of the sedimentary rocks over the flanks of the pre-Karoo basement topography which to a large extent controlled the propagation path of the main sill. Evidence established in this study suggests the effect of basin tectonics to be the overriding controlling factor of the stratigraphic position of the main sill in the Vryheid Formation sedimentary rocks of sequence of succession of the south-eastern Witbank Coalfield. Other factors i.e. the influence of the Ogies Dyke and syn-tectonic related regional scale structures seem to have had some control in the propagation paths of the associated offshoots of the main sill.
Open Access
Petrochemical characterization of dolerites and their influence on coal in the Witbank Highveld Coalfield, South Africa
(University of the Free State, 2008-08) Du Plessis, Johannes Jochemus; Van der Westhuizen, W. A.
A study was firstly conducted on the mineralogy and geochemistry of the dolerites, secondly on sedimentological controls (syngenetic) on coal deposition and diagenesis to gain a better understanding of the environment of the coal deposition and thirdly, the metamorphic influence of dolerite intrusions (epigenetic) on coal. The Ogies Dyke is the only intrusion found in the study area at Optimum Colliery. The absence of dolerite sill intrusions in this area made it possible to study coal deposition and diagenesis. It was to investigate the behaviour of a 20m thick bifurcating dolerite sill (the Witbank sill) and its associated metamorphic influence which occurs in the other Koornfontein, Bank and Goedehoop Collieries. The most prominent structure, the Ogies Dyke, forms the northern limit of the study area and forms a very important part of the geochemical and mineralogical study. Thin section investigations revealed the involvement of plagioclase in both the Witbank and Sasolburg dolerite fractionation assemblages indicates that the fractionation processes must have occurred within the crust although within different depths. The absence of pyroxene phenocrysts in the B5 sill (Sasolburg) indicates that the fractionation took place at a pressure significantly higher than that at which the plagioclase and olivine microphenocrysts have formed. The high percentage olivine in the B4 sill (Sasolburg) indicates that these two sills originated from different magma sources. Plagioclase microphenocrysts in the B5 sill as oppose to the macrophenocrysts of the B4 sill concludes that the fractionation processes of the B5 sill must have happened deeper within the crust. This study engage with dolerites that crystallised rapidly, intermediately and slowly as the crystal sizes are directly related to magma cooling. Fine crystalline dolerites like the chilled margins and bifurcations tend to be more susceptible for alteration as opposed to the medium and coarse crystalline dolerites. The 40m thick, fine crystalline B4 sill has undergone the most alteration comparing to the B5 sill, Witbank sill and the Ogies Dyke. The differences identified during this study distinguish the Sasolburg dolerites from the Witbank sill and the Ogies Dyke. X-ray fluorescence techniques were used to analyse the dolerite samples from the study area. All the dolerites are falling in the “basic” group. The B4 – Sasol dolerite sill is a high-MgO (picritic) basalt while the rest are basalts. The chilled margins of the bifurcations have an arithmetic mean of 4.89% MgO and the Ogies Dyke has 4.9% MgO and can be classified as evolved basalts. Lower MgO and Ni values in the Witbank bifurcations comparing to the Witbank sill indicate that the bifurcations are more evolved. The basaltic and evolved basalts can further be divided into low and intermediate K2O concentrations. A higher K2O concentration is placing the Ogies Dyke in the intermediate-K2O group whilst the Witbank sill (interior and chilled margins), and the Witbank bifurcations (interior and the chilled margins) are all falling in the low-K2O group. Two of the Witbank bifurcations (interior) having intermediate-K2O concentrations and are associated with the Ogies Dyke. The picritic B4 sill (Sasol) is also classified as a low- K2O dolerite. Considering K2O and MgO element concentrations the samples are falling in three categories, from evolved to picritic with the majority in the basaltic field. Borehole information was used to conduct isopach and isopleth maps of the pre-Karoo topography, floor elevation and thickness distribution, coal parameters and statistical data of various coal seams to underpin the sedimentological controls (syngenetic) on coal deposition and diagenesis The undulated platform onto which the No. 2 Upper Coal Seam formed at the Optimum study area had a major influence on coal grade. Thicker coals were deposited in the lower lying areas while they were thinning towards palaeohigh areas. Significant values indicate that the thinner coals are higher in ash (air-dry), lower in VM (daf), lower in CV MJ/kg (air-dry) and higher in relative density comparing to the coals deposited in the lower lying areas of the palaeovalley. Lithological descriptions from boreholes and structural interpretations in geological crosssections revealed the presence of a green 20m thick, bifurcating dolerite sill that intruded into the Vryheid formation of the Karoo Supergroup. It is associated with ±20m displacement and metamorphism on coal which is putting major constraints on coal mining in general. The metamorphic influence of the coal is largely restricted to the width of the contact aureole. The nature of the aureole depends on the geometry, variation in thickness and bifurcation of the sill. It is also found that the metamorphic contact aureole is much more extensive in the displaced and uplifted coal seams comparing to those beneath the sill. Moisture (ash-free) of the proximate analyses, volatile matter (daf), CV (daf) and approximated ash yield (AD) isopleth maps show that the dolerite sill caused a localised increase in rank. Areas of high moisture (proximate analyses moisture content) correspond to devolatilised areas, which are higher in ash and therefore having lower CV’s and are adjacent to known intrusions.
Open Access
Hydrogeochemical determination of the salt load from copper mine waste in the Bushveld igneous complex
(University of the Free State, 2008-11-28) Moukodi, Georges Pascal; Usher, Brent H.
This dissertation characterised geochemically waste from a copper mine in the Bushveld Igneous Complex, coupled with hydrochemical interpretations. In the first part of the dissertation, the methods involved in the quantification and qualification of mine acidic drainage were discussed. This included paste and rinse pH, Acid and Base potentials, net neutralisation potentials and neutralisation potential ratio. These methods form what is known as Acid-Base Accounting, (ABA). In the second part of this dissertation, the sampling methods and representativeness of the samples were discussed. All these methods are scientifically justifiable as they are in agreement with methods used internationally. In the third and most important part of this dissertation, results where discussed and proven to correlate with visual estimates from the field. In sulphides-containing waste material, Acid Mine Drainage (AMD) is produced due to the ingress of oxygen and water mainly from rainfall, and thus subsequent oxidation of sulphide-bearing minerals with the help of bacteria. However, in the presence of sufficient neutralisation potential, alkaline drainage is favoured as carbonated minerals (mainly dolomite and calcite) buffer the acidity. For this study, copper sulphide is recovered from foskorite ore imbedded with carbonatite which helped at the non acidification of the mine site. In the dissertation, the geochemical software PHREEQC was used and it confirmed that many silicates and alumino-silicates minerals are dissolved in the groundwater. This is an important finding as the presence of silica is an indication that substantial amount of acidity could have been released. This also constitutes reasonable evidence for the fact that chalcocite and covellite which are the main sulphides of copper mined on site can be considered as “weak” sulphides unlike pyrite which can be more severe to the environment. The software PHREEQC also confirmed that dolomite and calcite control the pH of the water, thus only fairly alkaline values in the range of pH 8 to pH 9.5 are expected on site. With visual investigations, it has been noticed that natural vegetation is taking place around the site even on the most hostile tailings like the magnetite. This is a very important aspect as positive outcome is expected for the fauna after mine closure. The following serve as recommendations: - The neutralisation processes release sulphate into the groundwater, and it is recommended that tracer tests methods be conducted to estimate the travelling time of the salts. - It is also recommended that the mine speed up the re-vegetation process as many animals cross the Kruger National Park to feed themselves within the mine. - It is recommended that more regular monitoring on boreholes be conducted as many dataless. Also it is suggested that anomalous boreholes be investigated, geochemically logged and re-sampled to verify or determine likely origins and interactions. - For further research, standard values of salt loads should be implemented so as to compare acceptable values with abnormal values. - The study of ABA using static tests should always be coupled with the humidity cells methods. While the former provides with the probability of acid formation, the latter provides with the reaction rates. - Additional studies should be conducted exclusively outside the mine to corroborate with the results from inside the mine.
Open Access
Reconstruction of contact metamorphism of the Uitkomst Complex, near Badplaas, Mpumalanga Province, South Africa, based on mineralogical and petrological investigations of the contact aureole
(University of the Free State, 2009) Kirste, Jens; Gauert, Christoph; Van der Westhuizen, Willem
This study presents petrological, mineralogical and geochemical data from the country rocks surrounding the basic to ultrabasic Uitkomst Complex in the Mpumalanga Province, South Africa. The investigations resulted in a isograde map based on the determination of critical mineral reactions for different lithotypes, i.e. the Timeball Hill Shale, Bevets Conglomerate and the Malmani Dolomite. Several minerals occurring in the metamorphic aureole, for example almandine in the Timeball Hill Shales, allow to determine temperatures and to a lesser degree pressure prevailing in the country rocks during the emplacement of the Complex. Geochemical profiles perpendicular to the contact into the country rocks indicate moderate enrichment of Mg, Fe, Cr and Ni close to the contact, levelling out to threshold values within 50 m distance from the contact. Additionally to the thermometric aspects of this thesis, an appraisal of the possible applications of corundum is given. The Uitkomst corundum shows, in parts, gem quality. Sapphire has been found in the Timeball Hill Shales south of the Complex. The corundum-bearing hornfelses are found in a distance of approximately 240 – 270 m from the contact in north-easterly and south-westerly direction. The rocks in this zone are characterized by a under-saturation of SiO2 and an elevated Al2O3-activity; the required temperature of corundum formation lies above 400 °C on average.
Open Access
Mineralogical and geochemichal investigation of Uranium conglomerate ores of the dominion reef group, Western Witswatersrand, South Africa
(University of the Free State, 2009-02) Rantzsch, Ulrike; Gauert, Christoph. D. K.; Van der Westhuizen, Willem. A.
English: Throughout the thesis, the genesis of the Dominion Reefs as Au-U placer deposits with particular focus of their paragenetic sequences whose detrital and/or hydrothermal origin was investigated. Dominion conglomerate Reefs are composed of quartz pebbles and detrital heavy minerals supported by an argillaceous matrix of illitic-chloritic composition. Geochemistry and mineralogy of two distinct Reefs has been characterized using petrographic studies, various whole rock geochemical analyses, and electron microprobe analyses.XRF analyses yield numerous results. Dominion conglomerates could be classified as sublitharenite, litharenite, and Fe-sands by major element geochemistry. The heavy mineral paragenesis (garnet, pyrite, monazite, zircon, chromite, magnetite, ilmenite, and phases containing uranium and thorium) suggests that the source of sediments is most likely similar to Archean granite-greenstone terrains. For tectonic setting of the sediments a passive margin and continental rift setting can be considered. Provenance investigation based on REE analysis suggests sedimentary recycling of felsic- and upper continental crust material as source rocks. Furthermore, the evaluation of geochemical data using the Pearson correlation coefficient suggests relationships of identified minerals. Elements, hosted in detrital minerals show a good correlation as well as elements hosted in hydrothermal- or hydrothermally altered minerals.Petrographic and SEM observations provided the opportunity to discriminate different generations of U-bearing minerals present in the Reefs. The chemical composition of U-bearing minerals can be correlated with their origin. Preserved uraninite sub-rounded grains occur associated with the primary detrital heavy mineral paragenesis. Moderate to high Th content (up to 9.30 wt% ThO2) of uraninite grains provided by EMPA support their magmatic origin. All uraninite identified are of detrital origin. Moreover, the chemical results allow distinguishing two individual groups and suggest that uraninite grains have been extracted from at least two distinct granitic or pegmatitic sources. However, the majority of U mineralization is represented by re-crystallized phases as secondary uranium bearing phases (pitchblende without Th), coffinite, U-Ti and U-Th phases occurring with the uranium redistribution by later hydrothermal processes.LA-ICP-MS analyses revealed a distinct age of 3100 ± 90 Ma for the primary mineralisation. The initial stage involved the placer development with deposition of detrital uraninite and related minerals. The younger age of 2700 ± 100 Ma as hydrothermal fluid event is recognised in the geochronological data, which correspond in time to the extrusion of the Ventersdorp lavas at ~2720 Ma. In this stage hydrothermally growth of mineral phases including secondary U bearing phases, galena and other minerals occurred.
Open Access
The geochemistry of the dykes in the Carletonville Goldfield
(University of the Free State, 2009-11) Litthauer, Alida; Van der Westhuizen, W. A.; Tredoux, M.
Numerous dykes traverse the Witwatersrand Supergroup rocks in the Carletonville Goldfield. The aim of this study was to investigate a classification system for the dykes. Samples were obtained from Tau Tona and Mponeng mines as well as from AngloGold Ashanti’s field office. The mineralogical investigation revealed that most dykes, with the exception of the Brazil dyke, are altered. The most abundant minerals are chlorite, actinolite, epidote, quartz and albitised and/or saussuritised feldspar, corresponding to a greenschist metamorphic facies mineral composition. Veins are commonly filled with quartz, calcite, epidote and chlorite, with sulphides and Fe oxides occurring occasionally. However, mineralogical heterogeneity as a result of different degrees of alteration, were found between samples from the same dyke. This heterogeneity may be an important consideration where rock engineering is concerned as it could cause different sections of the same dyke to have different physical properties Geochemical separation of the dykes into different groups was achieved by means of Bowen’s (1984) TiO2 v Zr and Zr/P v P/Ti plots as well as Linton’s (1992) discriminant plot. These same plots were employed in order to classify the dykes according to geochemical data taken from literature for four igneous events, namely, the Ventersdorp Supergroup, Transvaal Supergroup, Bushveld Igneous Complex and Karoo Supergroup, as well as geochemical data for dykes from the East Rand Proprietary Mine. Rare Earth Element patterns from the dykes were compared to literature data for the above-named igneous events in order to obtain a better classification.
Open Access
A mineralogical and geochemical study of seven meteorites from Malawi, Namibia and Lesotho
(University of the Free State, 2010-06) Lombard, Annegret; Tredoux, M; Schoch, A. E.
English: Seven meteorites from Malawi, Namibia and Lesotho were studied using optical microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry and electron microprobe analysis of mineral phases. Induced coupled plasma spectrometry and X-ray fluorescence techniques were used to obtain chemical information. The Thuathe meteorite from Lesotho is a H4 ordinary chondrite according to major element chemistry and mineralogy. The shock features were classified as S2/3 and the weathering grade as W0. It contains Sb sulphides, which had not been previously reported in any chondritic meteorite. Berthierite and stibnite was observed under the SEM and confirmed by electron microprobe analyses. The chondrite normalised REE pattern is relatively flat with no significant LREE/HREE variation. Very slight enrichment of Ta and U compared to H-group chondrites are noted. In this study the Machinga meteorite from Malawi is classified as an E6 ordinary chondrite according to major element chemistry and mineralogy, and the shock features were classified as S4, moderately shocked. Previously it had been classified as an L6 chondrite (Graham et al, 1984 and Koeberl et al, 1990). The rare earth element pattern is relatively flat with slight LREE/HREE variation from the norm. Slight enrichment of W, Pb and U is noted. The Balaka meteorite from Malawi is a L6 ordinary chondrite that is weakly shocked (S2). These classifications were done with major element chemistry as well as the mineralogy of the meteorite. The rare earth element pattern is flat with nearly no variation between LREE and HREE. The normalised trace element diagram mirrors the trends of the trace element diagram of the L-group chondrites with respect to ordinary chondrites. The Chisenga meteorite from Malawi is an IIIAB medium octahedrite according to chemistry and the bandwidth of kamacite (~1.5 mm) and taenite. Kamacite is the dominant Fe/Ni phase and Widmanstätten texture is prominent. The unreported specimens from Asab in Namibia prove to be L6 ordinary chondrites according to major element chemistry and mineralogy. The shock features are classified as moderately shocked (S4) and the weathering grade is W2. The rare earth element spectrum for the sample 1 from Asab shows enrichment of LREE. Enrichment of Ba, Sr, Th and U is shown in this sample. Sample 2 from Asab shows slight La enrichment compared to L-group chondrites. Enrichment in Ba, Sb, Sr and U is shown in the chondrite normalised trace element diagram. Sample 3 from Asab displays a flat chondrite normalised REE pattern with nearly no variation between LREE and HREE. Chemical variation in these meteorite samples in the chondrite normalised trace element diagram shows enrichment of Ba, Sb and Sr. The general trends of the diagrams are similar indicating that the three unknown specimens are of the same fall.
Open Access
A sedimentological investigation of the B-reef at Masimong 5 Shaft
(University of the Free State, 2010-08-04) Van den Heever, Michael Botes; Nel, L.
English: The ultimate objective of all exploration within the Witwatersrand Basin is to locate concentrations of gold which can be exploited economically. Gold in the B placer has high variance. The gold present in the B placer consists of small heavy detrital particles which are contained in the sedimentary host rock. In order to interpret the variable distribution of the gold within the B placer, cognisance must be taken of the sedimentological framework. The aim of this study was to employ a different approach to acquire an insight into the nature of the B placer and to shed more light on the depositional environments that played a major role during the formation of the B placer. Pebbles of the B placer conglomerates were investigated macroscopically in order to determine localities of possible gravel bar formation within the B placer. It was established that the B placer represented a braided river system with three different depositional environments, namely a fluvial environment, braid plain and a braid delta environment. The Upper Shale Marker at Masimong 5 Shaft played a major role in the development of these different depositional environments. The B placer remained river dominant and neither tide nor wave-related processes had an overwhelming influence on the system. The extreme fluvial dominance of the B placer improved the sorting of the braided delta system. The degree of reworking of the gravel bars in the braid delta by waves and current action resulted in the formation of thicker and better sorted conglomerates which, in turn, led to the formation of the B1 facies. Reworking and re-sedimentation of the B1 conglomerate occurred in the subaqueous setting. The B3 facies present at Masimong 5 Shaft were deposited in a purely fluvial braided environment. The improved perceptive of the B placer made it possible to identify four potential scenarios for the development of gravel bars within the braided river system, namely channel junctions, point bars, side bars or lateral bars; midchannel bars and barrier bars.